X-Ray Crystal Structure Analyses of Unstable Triplet Carbenes and Nitrenes and Comparison with their Reactivities

为了了解化学反应的机理，获得反应中间产物并分析它们的特性是必不可少的。虽然光谱研究已经弄清楚了激发态分子在几飞秒的时间尺度上的能量变化，但激发态分子的结构至今还不清楚，因为人们认为不可能将激发态分子捕获到晶格中并用X射线分析其结构。在目前的工作中，我们打算分析不稳定物种的结构，如三重态卡宾和硝烯。用氮气流动法在衍射仪上将反应物分子重氮甲烷或苯肼的晶体冷却到80K以下，并用导流管将其暴露在高压汞灯下。对低温辐照后的样品进行了衍射数据的采集。在差值傅里叶图中，出现了新的峰，这些峰被指定为所产生的ca…。虽然只有10%的反应物分子被转化为不稳定的物种，但更多的是Rbene或Net。计算结果与理论计算结果吻合较好。对于氮化物，由于生成的氮化物在晶格中与反应物分子重叠，很难得到精确的结构。主客体络合物是以二苯甲胺为主体生成的。辐照后的晶体用安装在春八号上的真空相机进行了分析。从主客体络合物中得到了硝烯的精确结构。此外，铂络合物的晶体在80K下被氙灯照射。收集了辐照前和辐照过程中的衍射数据，并对两种结构进行了分析。在辐照过程中晶格常数发生了明显的变化。辐照过程中的结构清楚地表明，根据分子轨道理论，在激发态时铂-铂距离缩短。以上结果表明，在不久的将来，X射线结晶学将在不稳定物种的分析中发挥重要作用。较少

In order to understand the mechanism of chemical reactions, it is essential to obtain the reaction intermediates and to analyze their characteristics. Although the spectroscopic studies have been made clear the energy change of the excited molecules in the time scale of a few femtosecond, the structures of the excited molecule have been obscure till now, since it has been considered to be impossible to trap the excited molecules in a crystalline lattice and to analyze the structures by X-rays. In the present work, we intended to analyze the structures of unstable species such as triplet carbenes and nitrenes. The crystal of the reactant molecule, diazomethane or phenylazide, was cooled below 80 K on the diffractometer using the nitrogen-gas-flow method and was exposed to the high-pressure mercury lamp using a guide tube. The diffraction data were collected after the irradiation at low temperatures. In a difference Fourier map, the new peaks appeared, which were assigned the produced ca … More rbene or nitrene, although only 10% reactant molecules were converted to the unstable species. The structures are in good agreement with those obtained from the theoretical calculation. For the nitrene, it was difficult to obtain the precise structure, since the produced nitrene overlapped on the reactant molecule in the crystalline lattice. The host-guest complex was produced using dibenzylamine as a host. The irradiated crystal was analyzed by the vacuum camera set up at Spring-8. The precise structure of the nitrene was obtained from the host-guest complex. Moreover, the crystal of a platinum complex was exposed to a xenon lamp at 80K. The diffraction data before and during the irradiation were collected and both of the structures were analyzed. The lattice constant clearly changed during the irradiation. The structure during the irradiation clearly indicated that the Pt-Pt distance is shortened at the excited state in accordance with the molecular orbital theory. A11 the above results suggest that the X-ray crystallography will play an important role in analyzing the unstable species in near future. Less